Physics Lecture: Light and Optics in Arabic

# Physics ## Chapter (1) ### Light and Optics Dr. Mohamed EL-Henawey PhD, Physics Department, Faculty of Science Mansoura University ## Light and optics: - Light is electromagnetic waves travels with speed of C = 3 x 10⁸ m/sec. ### Reflection of light from a flat mirror: - It was...

# Physics ## Chapter (1) ### Light and Optics Dr. Mohamed EL-Henawey PhD, Physics Department, Faculty of Science Mansoura University ## Light and optics: - Light is electromagnetic waves travels with speed of C = 3 x 10⁸ m/sec. ### Reflection of light from a flat mirror: - It was known that when a light incident on a flat polished surface, the ray is reflected in such a way that the angle of reflection θ_r is equal to the angle of incidence θ_i. - **Laws of reflection are:** 1. The angle of incidence is equal to the angle of reflection. 2. The incident ray, the reflected ray, and the perpendicular to the reflecting surface all lies in the same horizontal plane. ## Refraction of light: - When light is incident on a transparent material, the light divides at the surface into two parts. One part of the light is reflected. The remainder of the light is transmitted through the material. The bending of a light as it passes from one medium to another is called refraction. - When ϕ < θ_i, we say that the optical density of the second medium is greater than that of the first medium. ### Index of refraction: * n = Speed of light in vacuum / speed of light in medium = C / V ## Refraction of light: ### Snell's law: - It is an expression that relates the angle of incidence to the angle of refraction for a light ray that passes from one optical medium with refractive index N₁ to another medium with refractive index N₂. - n₁ / n₂ = Sinφ / sinθ - or, n₁ Sinθ = n₂ Sinφ ## Internal Reflection: - When the light is propagate from higher dense medium to less dense medium, and if the angle of incidence is greater than a certain angle called the critical angle θ_c (the refracted light ray moves parallel to the boundary that θ₂ = 90° ), the light will not transmitted. That is for all θ_i ≥ θ_c, the light is entirely reflected at the interface which is known as total internal reflection. - In this case, using Snell's law we have n₁ Sinθ = n₂ Sinφ n₁ Sinθ_c = n₂ Sin 90 ## Internal Reflection: - Since, Sin 90 = 1 so, n₁ Sinθ_c = n₂ - θ_c = Sin^-1 (n₂ / n₁) ## The formation of images by lenses and mirrors: - **lenses:** - A lens is usually in the form of a circular piece or relatively thin glass whose surfaces are sections of spheres. ### Lenses: - **Types of lenses**: - Convex - Concave #### Converging lens: - The distance between the center of the lens and the focal point is called the focal length (f) and is measured in cm, and the power of the lens (F) is given by F = 100/f = Δ or m^-1 #### Diverging lens: - The distance between the center of the lens and the focal point is called the focal length (f) and is measured in cm, and the power of the lens (F) is given by F = 100/f = Δ or m^-1 ## The formation of images by lenses : - **Difference between Real Image and Virtual Image** - **Real Image:** - The image is due to reflection or refraction, when the light arises from an object and converges to a certain point. - The real image can be captured on screen as it is the result of actual intersection of ray of light. - The images are inverted. - Converging lens are used to produce the image. - Concave mirror is used to produce the image. - **Virtual Image** - The image produced when the light arising from an object appears to strike a certain point. - It cannot be captured on a screen as it is the imaginary intersection of ray of light. - The images are erect. - Diverging lens are used to produce the image. - A plane mirror or convex mirror is used to produce the image. ## The formation of images by lenses : - **Convex lens** can form both real and virtual images depending upon the position of object placed in front of lens. - **The concave lens** alone never forms a real image, regardless of where the object is located. ## Lenses: - **The lens Equation:** - 1 / x_o + 1 / x_i = 1/f - f: is the focal length of the lens, positive for converging lens and negative for diverging lens. - x_o: is the distance from the lens to the object, always positive (for a single lens). - x_i: is the distance from the lens to the image, positive if the image is on the side of the lens opposite the object, and negative if the image is on the same side of the lens as the object. ## Lenses: - **Magnification:** - It is defined by the ratio of the light of the image formed by a lens to the light of object. - M = h_i / h₀ = -x_i / x_o - h_o: is the height of the object, positive when the object is above the axis. - h_i: is the height of the image, positive when the image is above the axis. - **Angular Magnification:** - The magnification of an image when observed by the eye is the angular magnification T. - T = θ_image / θ_object ## The Mirrors: - A spherical mirror is a mirror which has the shape of a piece cut out of a spherical surface. There are two types of spherical mirrors: concave, and convex. ## Mirrors: - **Concave mirrors are converging mirrors.** - **Convex mirrors are diverging mirrors.** - **The focal length is half the radius of curvature** - f = r/2 ## Mirrors: - **Concave mirrors** can produce both real and virtual images; they can be upright (if virtual) or inverted (if real); they can be behind the mirror (if virtual) or in front of the mirror (if real); they can also be enlarged, reduced, or the same size as object. - **In a convex mirror**, the image of an object is always virtual and upright. ## Mirrors: - **The Mirror Equation:** - 1 / x_o + 1 / x_i = 1 / f - f: is the focal length of the mirror, positive for concave mirror and negative for convex mirror. - x_o: is the object distance from the mirror, always positive. - x_i: is the image distance, positive if the image is on the same side of the mirror as the object, and negative if the image is on the side opposite to the object. - **Magnification:** - M = h_i / h₀ = -x_i / x_o ## Examples: - **Example (1):** A light ray is incident at angle of 25 on the surface between air and water. What angle due the refracted ray make with the perpendicular to the surface when the ray is incident from (a) the air side, (b) the water side? Knowing that the refractive index of water = 1.333. - **Solution** - (a) Light incident from air to water n₁ = 1, n₂ = 1.333, θ₁= 25 n₁ Sin θ₁ = n₂ Sin θ₂ 1 x Sin 25 = 1.333 x Sin θ₂ θ₂ = Sin^-1 (sin 25 / 1.333) = 18.5° - (b) Light incident from water to air n₁= 1.333, n₂ = 1, θ₁= 25 n₁ Sin θ₁ = n₂ Sin θ₂ 1.333 x Sin 25 = 1 x Sin θ₂ θ₂ = Sin^-1 (1.333 x Sin 25) = 34.3° - **Example (2):** what is the critical angle for a water -Lucite boundary? & n (Lucite) = 1.4913 and n (Water) = 1.333. - **Solution** - The critical angle exists only for the case in which the light is incident from the medium with the greater optical density to the medium with lower optical density and this mean that - n₁ = n (Lucite) = 1.4913 - n₂ = n (Water) = 1.333 - So, - θ_c = Sin^-1 (n₂ / n₁) - θ_c = Sin^-1 (1.333 / 1.4913) = 63.4° - **Example (3):** An object is placed 12 cm to the left of a lens that has a focal length of 8 cm. where is the image located? - **Solution** - Inserting x_o = 12 cm and f = 8 cm into lens equation, we find - 1 / x_o + 1 / x_i = 1 / f - 1/12 + 1/x_i = 1/8, so 1/x_i = 1/8 - 1/12 - 1/x_i = 3/24 - 2/24 - 1/x_i = 1/24 - So the image is located at a distance x_i = 24 cm (Real Image) from the lens. - M = x_i/x_o = 24/12 = -2 (Inverted Image) - **Example (4):** Suppose that the object in the preceding example is moved closer to the lens so that x_o = 6 cm. What is the new image distance? - **Solution** - 1 / x_o + 1 / x_i = 1/f - 1/6 + 1/x_i = 1/8, so 1/x_i = 1/8 - 1/6 - 1/x_i = 3/24 - 4/24 - 1/x_i = -1/24 - So the image is located at a distance x_i = -24 cm (Virtual Image) from the lens. - M = x_i / x_o = -24/6 = 4 (Upright Image (erect)) - The negative sign means that the image is on the same side of the lens as the object. ## Bioscience Essay (The Human Eye and Vision): - The human eye is a marvelous optical instrument has the following function: - It can produce sharp images for a wide range of object distances. - It can function over an extremely wide range of intensity. - It can detect small differences in color. - It requires very little maintenance. - It can define the stage of movement or of the rest of the objects. ## The structure of the Eye as Optical System: - **The sclera الصلب** covers everything except the **cornea القرنية** (The sclera is the outer protective coating of tough elastic tissue). - At the front of the eye, the sclera leads into the **cornea**, which is a transparent structure that admits light into the eye, its radius of curvature is nearly 0.8 cm. ## The Human Eye and Vision: - **Behind the cornea, there is a colored portion of the eye which is called Iris القزحية.** ## The Human Eye and Vision: - **Circular opening intermediate the Iris called Pupil بؤبؤ العين** through which the light enters the inner portion of the eye. The Pupil adjusts its size according to the intensity of the light falling on it, preventing overloading of the retinal System. - **The crystalline lens**, which is a convex lens and lies behind the Iris and its refractive index = 1.62. - **The ciliary الهدبي muscles** which attached the lens with the inner shape that has a greater or smaller curvature than the relaxed lens (this action is called accommodation). - **The aqueous humor خليط مائى**, it is a clear liquid filled the space between cornea and the lens. - **The vitreous humorالخليط الزجاجي**, It is a jellylike substance filled the space between the lens and the retina. - **The retina الشبكيه** is a sensitive membrane rich in blood-vessels أوعية دمويه and nerve fibers ألياف عصبيه (act as film or screen). The retina consist of a numerous number of sensitive elements or cells in the form of rods and cones. These elements convert light energy to electrical impulses نبضات which travel along the nerve fibers. ## The Human Eye and Vision: - **The fovea or the yellow spot**, it is the most sensitive part of the retina, it a small circle with a diameter of 0.025 cm lies at the intersection of the eye axis with the retina. Yellow spot contains cones which are responsible for color, whereas rods are responsible for dark and white light. - **The optic nerve العصب البصرى**, it is the collection of all fine fiber-nerves at the blind point. - **The choroid غلاف العين المشيمى** surface lies between the sclera and the retina, the front part of it called the Iris.